Refrigerating machine



Aug. 20, 1935.

M. J. AJAM REFRIGERATING MACHINE Filed July 28, 1951 3 Sheets-Sheet l g- 1935- M, J. AJAM 2,011,964

REFRIGERATING MACHINE I Filed July 28, 1951 I5 Sheets-Sheet 2 Aug. 20, 1935. M. J. AJAM 2,011,964

' v REFRIGERATING MACHINE Filed July 28, 1951 s Sheets-Sheet 5 Patented Aug. 20, 1935 v t UNITEDSTATES PATENT OFFICE REFRIGERATIN G MACHINE Mustafa J. Ajam, Waltham, Mass, assignor to Devon Manufacturing Company, Boston, Mass, a corporation of Massachusetts Application July 28, 1931, Serial No. 553,552

15 Claims. 01. 62-136) This invention relates to fluid compression apthe air may pass into a second dryer, which is paratus and more particularly to a refrigerating adapted to remove any moisture not removed by machine designed to use air or other gaseous the first dryer that is associated with the inlet of mediating fluid in a closed thermo-dynamic cycle. the make-up pump, and also to remove any mois- This invention is particularly directed to induc ture which may have been received from the oil 5 tion and drying arrangements for the mediating in the crank case. Preferably the air passing gas of a machine of this character, and is parinto the compression chamber is received in an ticularly applicable to refrigerating apparatus of annular space between theupper portion of the the character in the United States patent to compression piston and the cylinder wall, so that 0 Ivar Lundgaard No. 1,240,862. A machine of the any oil not removed from the incoming air 001- character disclosed in this patent is provided lects in a body in the lower part of this annular 'with a cylinder having a compression piston and chamber, and may flow past the piston into the 2 shifter piston, the latter being efiective to crank case. Such a flow of oil is induced, since transfer the mediating gas back and forth bethe gas within the cylinder is automatically maintween a compression chamber between the shifter tained by the induction arrangement at a mean 15 and compression pistons, and an expansion champressure higher than that in the crank case.

ber between the shifter piston and the cylinder Occasionally under unusual operating condihead. The gas moving between the compression tions, sufiicient moisture may find its way into the and expansion chambers passes through heat cold head of a machine of this character to cause exchangers and a regenerator or heat interthe formation of frost. It is difl'icult to melt this 20 changer. The present invention afiords an arfrost and to remove the resultant moisture from rangement which is particularly effective in perthe air within the machine without disassembly mitting the continued maintenance of a body of the machine. The present invention provides of dry gas, such as air, at a predetermined supermeans built into the cylinder wall, which may atmospheric pressure within the cylinder, i. e., be connected to a suitable auxiliary dryer form- 25 in the compression and expansion chambers and ing a part of the service equipment. With this the passages therebetween. arrangement the normal direction of crank shaft This invention also is effective in permitting air movement is reversed, so that the cold head bethus to be maintained in the cylinder while avoidcomes the compression chamber and its teming the movement of oil into the small passages perature rises, thus rapidly melting the collected 30 between the compression and expansion chamfrost. The air may then be caused to flow bers, these passages being of a type which might through the auxiliary dryer, which collects the readily be clogged with a relatively small amount moisture. To permit this desirable result I arof oil. Furthermore, moisture removing factors range a suitable check valve in a passage between 5 or dryers'are provided to maintain the air within the compression chamber and the crank case, so the cylinder in a dry condition, so that the collecthat air will flow from the interior of the cylinder tion of frost is normally avoided, despite the low to the crank case, passing from the auxiliary operating temperatures of the air in the expandryer, and thus having its moisture removed. si c e nd adjoining the same. In order Ordinarily the connections for the auxiliary dryer 40 to attain these desirable results, I provide a check may be closed by suitable plugs, which are re- -!0 valve arrangement which may be adjustable and moved by the service man so that the passage in which permits the flow of gas from the crank case the cylinder wall can be connected to the auxilto the compression chamber. while preventing iary dryer when the special defrosting operation such a flow in the opposite direction. The gas is necessary.

may be supplied by a suitable make-up pump hav- In the accompanying drawings: 4.) ing an outlet into the crank case, such as that Fig. 1 is a. vertical section through an improved disclosed in the United States patent to Ivar machine embodying the principles of this in- Lundgaard No. 1,838,148. A dryer is associated vention, this section being taken in the plane of with the inlet of this pump. From the interior the crank shaft axis;

of the crank case, air may flow through the check Fig. 2 is a vertical section at right angles with 50 valve to the compression chamber, whenever that of Fig. 1;

pressure in the latter falls to a point enabling the Fig. 3 is an enlarged sectional detailed view,

opening of the valve. Preferably, the air thus showing the arrangement of the induction pasflowing through the check valve first passes into sage in the cylinder wall; and

a suitable oil separator. From the oil separator Fig. 4 is an enlarged sectional detail showing lit) the arrangement of the passage in the cylinder wall, which is employed for the special defrosting operation.

The accompanying drawings in general illustrate a refrigerating machine of the type disclosed in the above-identified patents to Ivar Lundgaard, this machine having a crank case I with an upstanding cylinder 5 and with a sump 2 below the crank case. The cylinder 5 comprises a lower section 1 integral with the crank case, in which the main or compression piston 8 reciprocates. Above the section I is a second metal section 9 surrounding the compression chamber and having vertical duct portions I separated by radial fins connecting inner and outer annular metal walls. Heat radiating fins I! are secured to the outer wall of the section 9 and a suitable port l3 connects the ducts ID with the interior of the, cylinder, i. e., with the compression chamber. An upwardly extending continuation [4 of the metal section 9 provides a bearing for the lower metal portion l5 of the shifter piston IS, the body portion of which is formed of heat insulating material. Surrounding the shifter piston I6 is a regenerator I'l comprising inner and outer rings of heat insulating material, such as bakelite, with a plurality of spaced and/or insulated metallic elements l9 disposed in the passage l9 between the inner and outer bakelite rings.

The upper ends of the passages between ele-- ments l9 communicate with the lower ends of may be circulated in the jacket of the cold head by a pump 23. A transverse beam 22 engages the top of the cold head and is connected to tension elements 25 that engage lugs 24 upon the sides of the crank casing, thus clamping the various sections of the cylinder in firm engagement with each other.

During normal operation of this machine, as fully described in Patent No. 1,240,862, air is compressed between the pistons 8 and I6, flowing 4 through the passages ll) of cylinder section 9 and the regenerator II, this compressed air giving up heat through the fins l2 and to the separate elements IS in the regenerator IT. The compressed air as thus cooled is received in the cold head 20 and expands due to the downward movement of shifter piston l6, thus affording a refrigerating effect. Downward movement of piston 8 is then effective in drawing the air from the cold head back to the compression chamber, whereupon the cycle is repeated.

Various driving means may be employed for causing relative movement of the main and shifter pistons. As shown, for example, the crank shaft 30, which is driven through an exterior fiywheel 29, is provided with a central throw 3| having a connecting rod 32 articulated thereto and engaging a transverse pin 33 in a cylindrical member 34 that reciprocates in a cylindrical boss 35 which is vertically disposed at the center of the piston 8. The member 34 is connected by a vertical rod 36 with the lower metallic portion I5 of the shifter piston IS, a. bearing member 3'! being provided in the upper part of the boss 35 to guide the rod 36. of crank shaft 30 are throws ll with their crank the check valve 59, into the crank case.

At each sideof the throw 3 I axes in mutual alignment; as shown, the throw 3| may be disposed substantially 70 in advance of throws 4I. Connecting rods 42 are articulated to the throws 4| and engage wrist pins 43 which are secured to bosses in the outer wall of piston 8 and upon opposite sides of the central sleeve 35 respectively.

A packing ring I50 is disposed in normal engagement with the crank shaft 30 and a fixed gasket l 5|. Under normal conditions, the crank shaft is covered with an oil film, and the higher pressure within the crank case presses the -shou1- der with its oil film against ring I50, so that the latter firmly engages gasket l5l. Thus, this arrangement of parts cooperates with oil film to provide a substantially air-tight seal. An annularoil chamber I collects oil which leaks past the packing ring and gasket, and a duct ill in the crank case permits oil from chamber I10 to drain into the sump 2.

A machine of this character may conveniently be supplied with a make-up pump, indicated generally by'the numeral 50, which may be of the same type as that disclosed in Patent No. 1,833,148. This pump preferably is driven from a suitable portion of the piston driving mechanism, as shown, having its plunger 52 connected to an eccentric 5! at the end of the crank shaft 30. The pump comprises a suitable vertically disposed cylindrical housing 53 in which the plunger 52 reciprocates, a clearance chamber 55 being provided below the plunger 52. An inlet duct 54 is connected to the interior of the pump housing and communicates through a member 56 threaded into the lower part of the crank case with the upperpart of sump 2. A suitable screen 51 may be disposed on the lower end of member 56 with in the sump to prevent foreign matter from entering the inlet duct 54. A ball check valve 59 is disposed in an' outlet passage 68 connecting the clearance chamber 53 with the interior of the crank case below the normal level of oil therein, the valve opening when the pressure within the pump chamber is higher than that in the crank case.

A suitable dryer 65, which contains moisture absorbent material such as calcium chloride, phosphoric acid, or phosphorous pentoxide, may be disposed on the exterior of the machine, as shown in Fig. 2, having an air inlet 56 communicating with the outer air, and an air outlet 61 communicating with the upper part of the sump. When the level of oil in the sump is above the mouth of inlet duct 54, the make-up pump is effective in pumping oil, which is emitted through When the oil level falls below the inlet to the duct 51, the latter communicates with the exterior air through the duct 61 and the dryer 65. Under the latter condition, when the pressure of air within the crank case falls to a predetermined point, depending upon the adjustment of check valve 59, the pump 50 may be effective in drawing air through the dryer 65 and supplying the same to the interior of the machine.

The present invention particularly provides specific improvements in a machine of the general character described above, which permit the more satisfactory and efficient use of the mediating air while avoiding tendency of oil to find its way into the small passages l0 and I0 and between the elements I9, which may readily become clogged with oil'due to their small cross sections.

This invention further provides means to aid in the maintenance of the mediating air in a notmally dry condition and also special means to remove moisture, should the moisture content of the air accidentally rise sufiiciently to cause the formation of frost in the cold head. To permit these desirable results, I provide, as shown in Fig. 1, an oil separating chamber III which communicates with the interior of the crank case through an air passage II. This separator may conveniently be provided with a plurality of inwardly inclined staggered plates I2 (Fig. 3) which provide a tortuous air passage and which collect oil particles. A drain I3 connects the lower part of the separator I with the lower part of the crank case I, thus permitting the oil separated out of the air which flows into separator 10 to be returned to the crank case.

A duct I3 connects separator I0 with a second dryer 15, which may be similar to the dryer 65. The outlet pipe 11 connects the latter with a radially disposed passage I8 in the wall of the cylinder section I. Passage 18in turn communicates with a vertical passage 19. The latter is shown in greater detail in Fig. 3 and is provided with an enlarged upper portion 80 having a ball check valve 8| engaging a seat 82 and normally held in its closed position by a compression spring 84, the upper end of which engages a threaded plug 85 having a slotted end to receive a screw driver and to permit ready variation of the normal distortion of spring 84 when the valve is closed. A vent 86 connects the upper part 80 of passage 19 with the interior of the cylinder. v

When the machine is first started the air within the machine may be atmospheric pressure. The make-up pump 50 will then operate to draw air into the dryer 65 and thence into the sump, supplying the same to the interior of the crank case until the pressure therein has risen to a point determined by the relative maximum and mini-' mum displacements of the chamber 55 and the pressure with which the valve 59 is held against its seat. As the machine continues running, the make-up pump tends to maintain the interior pressure at this predetermined point. When air is first supplied to the crank case in this manner by the make-up pump, the mean pressure in the crank case will be higher than that in the compression chamber. Accordingly air flows through passage II, separator 10, dryer I5, duct 11, passages 19 and 86 each time the piston 8 moves downwardly toward the bottom of its stroke, thus admitting additional air under pressure to the interior of the cylinder. As the air is compressed in the compression chamber and expanded in the crank case due to the upward movement of piston 8, the valve 8| closes. Thus pressure is constantly built up in the cylinder until the mean pressure within the compression chamber is above the mean pressure in the crank case by a definite amount determined by the adjustment of the valve 8I. As the machine continues running there is a tendency for air to leak about the piston 8 and the plunger 36 from the compression chamber into the crank case. The arrangement of the by-pass valve 8|,

however, is effective continuously to compensate for this leakage and to maintain the desired higher pressure within the compression chamber. During temporary idle periods the air at higher pressure in the compression chamber tends to leak into the crank case so that these pressures may become substantially equalized by the time the machine again starts in operation. The arrangement of the valve 8|, however. permits the pressure within the cylinder automatically to rise cylinder normally is quite small.

so that the desired differential between the cylinder and crank case pressures is again created. It is thus evident that the arrangement of the valve 8| permits the mean pressure within the cylinder normally to be higher than that within the crank case and that after this pressure differential has been disturbed due to shutting down of the machinev the arrangement of the by-pass valve automatically permits the normal pressure conditions to be resumed. Thus the portion of the machine in which the mediating air is actually being used may contain this air at a higher average pressure than the portion of the machine from which any leaks are likely to occur, i. e., the crank case, from which there may be some slight leakage about the ring I50. When leakage thus occurs, the pressure within the crank case falls,

so that the make-up pump automatically operates to return the internal pressure of the machine to the desired point.

The upper part of piston 8 is of smaller diameter than the main body portion of the piston, thus providing an annular space 90 betweenthisportion of the piston and-the inner surface of the cylinder. Accordingly oil which has not separated from the air received from passage II flows under the action of gravity into this annular chamber 90. Due to the fact that the pressure within the cylinder is normally higher than that within the crank case, this oil tends to be forced downwardly between the piston and cylinder and thus be returned to the crank case. The upper part of bushing 31 preferably is provided with a bore of enlarged diameter, designated by numeral 31 so that it does not directly contact the rod 36. An oil groove I53 is disposed at the lower end of this relieved portion and radial passages I54 communicate with passages I55 in the ribs of the piston 8, that in I turn open into the space 90 about the upper part of the piston. Thus oil which is carried upwardby the plunger 36 is scraped off from the plunger by the lower edge of the groove I53 and flows downwardly through passages I54 and I55 to the space 90, from which the higher pressure above thepiston is eifective in returning the oil to the crank case. It therefore is evident that clogging of the air passages in ducts l0 and I0 and those of the regenerator wall is avoided.

' form in the cold head 20. The collection of frost in this region is clearly indicated by a distinct knock, since the clearance between the piston I6 at the top of its stroke .and the head of the Under these conditions it has heretofore proved difficult to remove the moisture collected in the form of frost in the cylinder head.

The present inventionaffords special means built into the cylinder wall which cooperates with an auxiliary dryer that may form a part of the service mans equipment to permit the ready performance of the defrosting operation and the removal of the moisture from the interior of the machine. For this purpose, as shown in Figs.

2 and 4, a vertical passage 92 is provided in the wall of the lower section I of cylinder 5, this passage having an enlarged upper portion with a check valve 94 therein resting upon a compression coil spring 95 which holds the ball against a seat on the bushing 91 threaded into the upper part of the section 1 and afiording communication between the duct 92 and the air passages in the interior of the cylinder wall as well as with the compression chamber. The passage 92 communicates with a threaded opening in the cylinder wall that normally has a threaded plug 94 in engagement therewith. A second threaded plug I engages a similar opening I02 below the opening 93 and communicates with a passage IOI extending downwardly in the cylinder wall and communicating with the interior of the crank case I.

When the defrosting operation and removal of moisture is to be effected, the plugs 94 and -I00 are removed and an auxiliary dryer I05 having an inlet duct I01 and an outlet duct I06 is connected to ihe machine. The ducts I00 and I0! are provided with unions I08 and I09 respectively which are connected to the threaded openings 93 and I02 respectively. Thus the passage 92 is made to communicate with the interior of the dryer I05 and the latter in turn communicates with the crank case.

When the auxiliary dryer I05 is thus connected to the machine, the direction of rotation of the crank shaft 30 is changed by any means, for example by a suitable arrangement of a twis' ed belt acting on the flywheel 29 so that the pis tons 8 and I6 reciprocate in directions opposite to their normal movements. This results in the compression of mediating fluid above piston I6 and its expansion below the sameso that the cold head 20 then becomes a warm compression chamber, its temperature rising so that the frost quickly melts. While the chamber between pistons 8 and I6 then becomes the expansion chamber, the temperature of this portion of the ap-- paratus does not fall unduly, due to the fins I2- which are exposed to the surrounding air. In many .installations of a machine of this character, a fan is arranged to blow air at room temperature over these fins. Accordingly the temperature within the chamber between the pistons does not fall sufliciently to cause any formation of frost, when the machine is thus being operated by reversed driving means. Since the check valve 94 opens in response to a higher pressure thereabove, when the piston 8 is in the upper part of its stroke, the air from the interior of the cylinder flows downwardly through the dryer I05 which removes the moisture from the air. The check valve 8| in the passage 19 is effective in permitting the ready return of the dried air from the crank case to the interior of the cylinder, so that as the machine operates in a reversed direction the air is circulated through the dryers I05 and I5, while the frost in the cold head 20 is changing to vapor. Thus the moisture is readily removed from the interior of the cylinder. When the moisture has thus been removed, the auxiliary dryer I05 is disconnected from the machine and the plugs 94 and I00 are replaced. The driving belt is then arranged to cause operation of the machine in its usual manner.

From the foregoing it is evident that I have provided a refrigerating machine employing air or similar gas as a mediating fluid which has 4 a special induction arrangement normally assuring the removal of moisture from the gas which is supplied to the machine to compensate for leakage. This induction means is arranged so that the mean operating pressure within the cylinder isnormally higher than that within the crank case from which leakage is more likely to take place. Thus the advantages of employing air at a relatively high working pressure are attained without entailing the necessity of guarding against leakage from such high pressure around the crank shaft.

The induction means is also particularly designed to prevent oil from finding its way into the small passages within the cylinder wall and thus cloggingthe same to prevent normal flow of air. While this induction arrangement is efiective in preventing the collection of an objectionable amount of moisture within the cylinder and consequent formation of frost in the cold head, I have provided means to facilitate the removal of such moisture should the same collect due to abnormal conditions or improper servicing of the dryers 65 and 15. Thus when the auxiliary dryer I05 is arranged to remove moisture under these unusual conditions the induction means cooperates therewith in permitting effective circulation of the air through dryers I05 and 75, thus facilitating the rapid removal of moisture.

It is therefore evident that the present invention is particularly advantageous in permitting the highly efficient employment of air at superatmospheric pressure as a mediating fluid within a refrigerating machine, permitting the air to be maintained in a dry condition or dried if it should become objectionably moist and preventing the interference of lubricating oil with the normal cyclic movement of the air.

It should be understood that the-present disclosure is for the purpose of illustration only and that this invention includes all modifications and equivalents which fall within the scope of the appended claims.

I claim:

1. Apparatus of the class described, comprising a crank case, a cylinder, a piston reciprocable in the cylinder, an inlet in the crank case,'a duct between the crank case and the interior of the cylinder above said piston, and valve means associated with said duct permitting the flow of fluid from the crank case to the interior of the cylinder in response to an increase in pressure within the crank case and a corresponding decrease in the pressure within the cylinder, said means preventing flow of fluid in the opposite direction.

2. Apparatus of the class described, comprising a crank case, a cylinder, a piston reciprocable in the cylinder, an inlet in the crank case, a duct between the crank case and the interior of the cylinder above said piston, and valve means associated with said duct, said means including a valve and a spring tending to close the valve, the valve means permitting the flow of fluid from the crank case to the interior of the cylinder in response to anincrease in pressure within the crank case and a corresponding decrease in the pressure within the cylinder, said means preventing flow of fluid in the opposite direction, and means for adjusting the stress on the spring to vary the pressure at which the valve will open to permit flow through the duct.

3. Apparatus of the class described, comprising a crank case, a cylinder, a piston reciprocable in the cylinder, an inlet in the crank case. a duct between the crank case and the interior of the cylinder above said piston, and valve means associated with said duct permitting the flow of gas from the crank case to the interior of the cylinder in response to an increase in pressure within the crank case-and a corresponding decrease in the pressure within the cylinder, said means preventing fiow of gas in the opposite direction, and an oil separator associated with said duct to prevent the passage of oil through the duct to the interior of the cylinder.

4. Apparatus of the class described, comprising'a crank case, a cylinder, a piston reciprocable in the cylinder, an inlet in the crank case, a duct between the crank case and the interior of the cylinder above said piston, and valve means associated with said duct permitting the flow of gas from the crank case to the interior of the cylinder in response to an increase in pressure within the crank case, and. a corresponding decrease in the pressure within the cylinder, said means preventing flow of gas in the opposite direction, and a dryer associated with said duct to remove moisture from the gas passing through said duct.

5. Apparatus or the class described, comprising a crank case, a cylinder, a piston reciprocable in the cylinder, an inlet in the crank case, a duct between the crank case and the interior of the cylinder above said piston, and valve means associated with said duct permitting the flow of fiuid from the' crank case to the interior of the cylinder in response to an increase in the pressure within the crank case and a corresponding decrease in the pressure within the-cylinder, said means preventing flow of gas in the opposite direction, a dryer associated with said inlet to remove moisture from gas entering the crank case, and a second dryerassociated with said duct to remove moisture received from the oil in the crank case.

6. Apparatus of the class described comprising a crank case, a cylinder, a piston reciprocating in the cylinder, a pump in the lower part of the crank case, said pump being arranged automaticall'y to feed air into the crank case when the internal pressure in said case falls below a predetermined point, said pump having an outlet normally immersed in an oil body in the lower part of the case, a duct communicating with the upper part of the case and with the interior of the cylinder, a check valve adapted to prevent flow through said duct from the cylinder to the crank case; and permitting flow from the case to the duct as the piston moves downwardly and increases the pressure in the case to a point above that in the cylinder.

7. Apparatus of the class described comprising a crank case, a cylinder, a piston reciprocating in the cylinder, a pump in the lower part of the crank case, said pump being arranged automatically to feed air into the crank case when the internal pressure in said case falls below a predetermined point, said pump having an outlet normally immersed in an oil body in the lower part of the case, a duct communicating with the upper part of the case and with the interior of the cylinder, a check valve adapted to prevent flow through said duct from the cylinder to the crank case, and permitting flow from the case to the duct as the piston moves downwardly and increases the pressure in the case to a point above that in the cylinder, and an oil separator associated with the inlet end of said duct to prevent oil passing therethrough into the cylinder, whereby the average pressure in the cylinder is higher than that in the case to prevent oil from passing between the cylinder wall and piston into the chamber above the piston.

8. Apparatus of the class described comprising a crank case, a cylinder, a piston reciprocating in the cylinder, a pump in the lower part of the crank case, said pump being arranged automatically to feed air into the crank case when the internal pressure in said case falls below a predetermined point, said pump having an outlet normally immersed in an oil body in the lower part of the case, a duct communicating with the upper part of the case and with the interior of the cylinder, a check valve adapted to prevent flow through said duct from the cylinder to the crank case, and permitting flow from the case to the duct as the piston moves downwardly and,

increases the pressure in the case to a point abdve that in the cylinder, and an oil separator associated with the inlet end of said duct to prevent oil passing therethrough into the cylinder, whereby the average pressure in the cylinder is higher than that in the case preventing oil passing between the cylinder and piston, said piston having an upper portion of reduced diameter to provide an oil collection space, wherein any oil passing through the duct may be pocketed.

9. Apparatus of the class described comprising a crank case, a cylinder, a piston reciprocating in the cylinder, a pump in the lower part of the crank case, said pump being" arranged automatically to feed air into the crank case when the internal pressure in said case falls below a predetermined point, said pump having an outlet normally immersed in an oil body in the lower part of the case, a duct communicating with the upper part of the case and with the interior of the cylinder, a check valve adapted to prevent flow through said duct from-the cylinder to the crank case, and permitting flow from the case to the duct as the piston moves downwardly and increases the pressure in the case to a point above that in the cylinder, and a dryer associated with pump inlet to remove moisture from air entering the crank case.

10. Apparatus of the class described comprising a crank case, a cylinder, a piston reciprocating in the cylinder, a pump in the lower part of the crank case, said pump being arranged automatically to feed air into the crank case when the internal pressure in said case falls below a predetermined point, said pump having an outlet normally immersed in an oil body in the lower part of the case, a duct communicating with the upper part of the case and with the interior of the cylinder, a check valve adapted to prevent fiow through said duct from the cylinder to the crankcase and permitting flow from the case to the duct as the piston moves downwardly and increases the pressure in the case to a point above that in the cylinder, a dryer associated with pump inlet to remove moisture from air entering the crank case, and another dryer in said duct between the separator and valve to collect moisture received from the oil.

11. Apparatus of the class described comprising acrank case, a cylinder having a head, a pair of pistons in the cylinder, and means for causing relative movement between the pistons, a duct connecting a chamber between the piston-s to a chamber between the outer piston and the cylinder head, a passage in the cylinder wall communicating with said duct, a check valve in said passage to permit flow away from the cylinder. a closure member normally threaded into the end of said passage remote from the duct, whereby the check valve is normally inoperative, a passage communicating with the crank case, and a closure normally closing the last-named passage but removable therefrom, said closures being removable to permit the connection of drying means to the opening normally occupied by the closures, whereby air may flow through the passage from the cylinder and thus through the dryer into the crank case.-

12. Apparatus of the class described comprising a crank case, a cylinder having a head, a pair of pistons in the cylinder, and means for causing relative movement between the pistons, a duct connecting a chamber between the pistons to a chamber between the outerpiston and the cylinder head, a passage in the cylinder wall communicating with said duct, a check valve in said passage to permit flow away from the cylinder, a c10 sure member normally threaded into the end of said passage remote from the duct, whereby the check valve is normally inoperative, a passage to permit air flow to the cylinder, and a dryer" associated with said induction duct, whereby air passing through said drying means to the crank case may pass through the dryer and return to the cylinder.

13. Apparatus of the class described, comprising a. crank case, a cylinder having a head, a

pair of pistons reciprocable therein and providthe cylinder.

ing a compression chamber between the pistons and an expansion chamber between one of the piston and cylinder heads, passages between said chambers, a duct between the first-named chamher and the interior of the crank case, and a check valve in said duct permitting fluid flow from the crank case to said first-named chamber.

14. Apparatus of the class described, comprising a crank case, a cylinder having a head, a pair of pistons reciprocable therein and providing a compression chamber between the pistons and an expansion chamber between one of the piston and the cylinder heads, passages between said chambers, a duct between the first-named chamber and the interior of the crank case, a pump connected to the crank case and arranged to maintain air therein at a predetermined mean superatmospheric pressure, and means associated with said duct to maintain air within the cylinder at a predetermined mean pressure higher than the near pressure in the crank case.

15. Apparatus of the class described comprising a crank case, a cylinder secured to the "crank case and having a head, a pair of pistons in the cylinder, and means for causing relative movement between the pistons, a duct connecting the chamber between the pistons with the chamber between the outer piston and the cylinder head, whereby relative movement of the pistons causes the movement of fluid through said duct between said chambers, a passage in the cylinder wall communicating with the interior of the cylinder including said chambers and said duct, a check valve in said passage to permit fluid flow away from the interior of the cylinder, and means normally closing the outer end'of the passage but movable to open the same so that fluid may fiow out of said chambers and duct to the exterior of MUSTAFA'J. AJAM. 

